Among human activities, CO2 emissions from electricity generation and industry make up 65% of global greenhouse gas emissions. Considering the world's growing energy demand and continued dependence on fossil fuels, there is an unprecedented need to develop technologies to significantly reduce CO2 emissions.
One promising means of reducing CO2 emissions is post-combustion CO2 capture and utilization (CCU), which transforms low concentrations of CO2 in emissions into high purity CO2 for utilization or disposal. However, implementation of these technologies, such as the chilled ammonia and monoethanolamine (MEA) carbon capture processes, has been limited to pilot plants due to enormous operating costs. The most effective prior art processes require elevated temperature heat, generally supplied by steam diverted from power generation, increasing electricity costs by over 70% in some cases. Elevated temperature heat constitutes>80% of the energy consumption in current carbon capture processes and is the costliest component of CO2 capture. A significantly lower operating and capital cost CO2 capture system is necessary to make CCU an effective means of reducing CO2 emissions.
Another means of reducing CO2 emissions is pre-combustion CO2 capture. Pre-combustion CO2 capture involves removing the carbon or carbon dioxide from fuel before combustion is completed. For example, pre-combustion CO2 capture may involve transforming natural gas and water into hydrogen and CO2 using steam reforming and water gas shift reaction, and subsequently separating said CO2 from said hydrogen before employing said hydrogen as a fuel. Pre-combustion CO2 capture, as well as other applications for acid gas separation, including, for example, CO2 separation from natural gas or biogas, employ separation technologies based on physical absorption, chemical absorption, gas phase membrane separation, or adsorption. Physical absorption CO2 separation technologies involve pressurized absorption of CO2 into an inert solvent, such as water or an organic solvent, then the desorption of CO2 under reduced pressure conditions, often with the application of heat. Prior art physical absorption CO2 separation technologies consume significant electricity in the compression or pressurization of the acid gas laden gas stream and the electricity required to pump the relatively substantial amounts of liquid throughout the separation process. Current physical absorption CO2 separation technologies absorb acid gas in the same liquid reagent composition and liquid phase as they desorb acid gas. As a result, a trade-off occurs—the more soluble acid gas is in a physical solvent, the more energy that is required during desorption to regenerate the physical solvent; the less soluble acid gas is in a physical solvent, the more energy that is required during the pressurization/compression during absorption. Furthermore, in prior art technologies, solubility change or absorption or desorption almost entirely driven by changing the partial pressure and/or temperature of a liquid, while the solubility parameters or properties of the liquid itself remain unchanged.
Pure CO2 is a valuable product with 80 Mt per year commercial market. Due to the cost prohibitive nature of current CO2 capture systems, over 80 percent of the demand for pure CO2 is supplied by the unsustainable drilling of CO2 source fields, which contain CO2 that has been sequestered for millions of years. An effective system that captures CO2 from flue gas below market prices would at least partially displace the pure CO2 production from these unsustainable and counterproductive sources.
Advantageously, the present invention pertains to new highly efficient, low energy, and low-cost systems and methods to separate gases such as an acid gas (e.g., one comprising CO2), a basic gas, a hydrocarbon, an inert gas, air, or a combination thereof. In one embodiment the invention involves a process for separating gas comprising absorbing one or more gases in a liquid system comprising one or more physical solvents, wherein said one or more physical solvents comprise one or more liquid phases in the liquid system. The conditions are controlled to change the number and composition of liquid phases in said liquid system. The system may exhibit a phase transition at a lower critical solution temperature, upper critical solution temperature, or both. Said phase transitions may result in a change in the equilibrium solubility or kinetics of absorption or desorption, or combination thereof of one or more gases in one or more liquid phases.
In another embodiment, the invention involves a process for separating gas comprising absorbing a first gas and a second gas with a one phase liquid solution and changing the one phase liquid solution to a second liquid solution comprising two or more phases wherein one phase of the two or more phases is selective for said first gas relative to said second gas.
In another embodiment, the invention involves process for separating gas comprising absorbing a first gas and a second gas with a liquid solution comprising two or more phases and transforming the two-phase liquid solution to a second liquid solution comprising one phase wherein the second liquid solution is selective for dissolving said first gas relative to said second gas.
In another embodiment, the invention involves a process for separating gas comprising absorbing one or more gases with a liquid solution comprising one or more physical solvents; mixing an antisolvent with said liquid solution to form a second liquid solution; desorbing at least one gas from said second liquid solution; and treating at least a portion of said second liquid solution with one or more membranes to separate antisolvent from said one or more physical solvents. These and other embodiments are described in detail below.